The present invention relates to a cruising control device for vehicles, such as automobiles, which controls the driving force characteristics of the vehicle in accordance with the traveling information of the vehicle.
Recently, a load-information display apparatus, namely, navigation systems has come into wide use for vehicles, such as automobiles. Further, the recent vehicles are in course of carrying a cruising control device that controls the driving-force characteristics so as to accord with a cruising road, on the ground of information brought by the navigation system.
In the current navigation system, the vehicle position is estimated by employing a satellite navigation to calculate the vehicle position on basis of signals from a GPS satellite and a self-support navigation to calculate the vehicle position on basis of velocity pulses and gyro-signals, together. Further in the navigation system, there is also carried out a so-called xe2x80x9cmap matchingxe2x80x9d where the vehicle position is mated with the present road map in view of removing display errors on the map.
FIG. 5 illustrates the basic principles of map matching. Based on GPS measurements, vehicle speed pulses and gyro-sensor outputs, it is first executed to calculate both the present vehicle""s position PX (on estimation) and traveling direction D. Nevertheless, since the so-calculated position PX and traveling direction D are not always included in a road existing on the map, it is next executed to determine a road R on which the vehicle is estimated to be traveling. This is the very function called xe2x80x9cmap matchingxe2x80x9d.
In detail, it is first executed to select the road R in the vicinity of the present position PX from the map data and subsequently calculate a distance xcex4 between the road R and the position PX. Next, it is carried out to calculate an angular difference "THgr" between the calculated traveling direction D and the selected road R. Here, if the so-obtained values xcex4 and "THgr" are less than predetermined reference values together, it is judged that the vehicle is now traveling on the selected road R and therefore, the vehicle position is corrected for a position PO.
In case of existing a plurality of roads near the point PX, then there will be selected one of the roads, which is the closest to the point PX and also has the smallest angular difference "THgr". By repeating the above processes at predetermined intervals, it allows the map matching to be realized, so that the present vehicle position is displayed on the specified road in the map.
In the map matching process mentioned above, however, there sometimes arise problems that the accuracy of satellite navigation is deteriorated since the receiving sensitivity of the GPS satellite is reduced due to an environment about the road and that the accuracy of self-support navigation is deteriorated by errors in the traveling-distance calculated from the vehicle speed pulses, due to the expansion of tires at the vehicle""s traveling at a high speed.
Then, since the above point PX and traveling direction D are greatly deviated from the rightful road position PO and road direction respectively, the map matching process is impossible of judgement which of the roads should be matched with the above point PX, causing a result of no road coming under the point PX and traveling direction D.
Further, there is a possibility that an accurate traveling direction of the vehicle is not determined upon judgement that the vehicle is whirling round while that the vehicle is abruptly turning right or left, causing a phenomenon of impossible map matching.
Additionally, as shown in FIGS. 6A and 6B, if the vehicle is subjected to its undershoot (FIG. 6A) or overshoot (FIG. 6B) during the vehicle""s turning left or right at intersection, then the navigation system may judge that the system is now impossible of map matching (i.e. failure of map matching). Alternatively, when the vehicle turns sharp after it has been traveling on a straight line of freeway for a long time continuously, the navigation system also judges that the system has a failure of map matching, causing a phenomenon that the vehicle position on display is deviated from a road that the vehicle is actually traveling on.
Meanwhile, in a vehicle cruising control device where the vehicle""s driving force characteristics is controlled on the ground of the present road property information (e.g. traveling on freeway or narrow lane, etc.) while employing the road information brought by the above navigation system, if the above-mentioned problem (i.e. failure of map matching) arises in the navigation system, then the vehicle cruising control device cannot obtain a designated information about the road property.
In order to cope with such a problem, Japanese Patent Publication (kokai) No. 10-184413 discloses a cruising control device that then takes measures of prohibiting the control itself; changing the frequency of controls; replacing the control with other control pattern; and so on.
However, when the vehicle repeats right and left turns on the roads in a grid pattern or the vehicle travels continuous curves, such as mountain pass road, there is a possibility that the judgement of failure of map matching occurs often. Consequently, a problem arises in the above-mentioned prior art device that the driving-force control pattern of the vehicle is frequently altered so as to produce a sense of incompatibility in the vehicle""s behavior.
Under the above circumstance, it is an object of the present invention to provide a vehicle cruising control device that does not produce such a sense of incompatibility in the vehicle""s behavior in spite of the failure of map matching.
According to the invention, the above-mentioned object is accomplished by a vehicle cruising control device for a vehicle, comprising:
a road property detecting unit for detecting a road property of a road on which the vehicle is traveling; and
a driving-force control unit for controlling driving-force characteristics of the vehicle in accordance with the detected road property,
wherein, when the road property detecting unit is impossible to detect the road property, the driving-force characteristics of the vehicle on the ground of the road property which has been detected before the road property detecting unit becomes impossible to detect the road property.